1. Technical Field
The present invention relates generally to a fuel injector for internal combustion engines, and more particularly to an improved nozzle structure of a fuel injector designed for establishing fine atomization of fuel.
2. Background of Related Art
In recent years, the exhaust emission regulation of automotive vehicles has been tightened, requiring fine atomization of fuel to be injected into the engine. In order to meet this requirement, there have been proposed some fuel atomization mechanisms including a nozzle plate which is disposed downstream of a valve seat formed in a valve body and which has formed therein spray holes designed to be suitable for atomization of fuel spray.
FIGS. 11 and 12 show one example of conventional fuel injectors. The shown fuel injector is designed to move a valve head 125a formed on an end of a needle 125 into and out of engagement with a valve seat 126a formed in a valve body 126 for closing and opening a fuel nozzle. The fuel injector includes a nozzle disc 130 attached to an end 126b of the valve body 126. The nozzle disc 130 has formed therein four spray holes 130a, as shown in FIG. 12, for atomization of fuel sprays.
The above fuel injector, however, has the drawback in that the nozzle disc 130 is made of a thin plate and, therefore, the fuel injection pressure causes the nozzle disc 130 to be deformed outward, thereby leading to the formation of an air gap between an inner surface 130b of the nozzle disc 130 and the end 126b of the valve body 126. This will cause the fuel to enter the air gap partly, resulting in change in spread of fuel sprays and decrease in amount of the fuel injected.
In order to avoid the above problems, it may be proposed to increase the thickness of the nozzle disc 130, however, the increase in thickness more than 1 mm will cause the depth of the spray holes 130a in a direction of the fuel injection to be increased undesirably, thereby leading to the accumulation of fuel in the spray holes 130a, which, like the above, results in change in spread of fuel sprays and decrease in amount of the fuel injected.
The nozzle disc 130 is, as shown in FIG. 11, welded at locations 191 to the end 126b of the nozzle body 126 and, therefore, the welding heat is transmitted directly to the nozzle body, which may result in thermal deformation of the valve seat 126a, leading to the leakage of fuel into a combustion chamber of the engine even when the injector is fully closed. This will cause the amount of unburned hydrocarbon (HC) to be increased, leading to a greater concern about an increase in harmful emissions.
Japanese Patent First Publication No. 5-187341 discloses an improvement on a fuel injector for internal combustion engines, however, has the same problems set forth above.
International Publication Nos. WO92/03653 and WO93/02285 and Japanese Patent First Publication No. 6-26419 filed by the same applicant as that of the above publication No. 5-187341 propose measures for alleviating the above problem on the deformation of the nozzle disc 130.
Specifically, International Publication No. WO92/03653 and Japanese Patent First Publication No. 6-26419 teach a cup-shaped nozzle body having a greater rigidity instead of the nozzle disc 130. International Publication No. WO93/02285 discloses a support plate which urges a nozzle disc into constant engagement with an end surface of a valve body.
The cup-shaped nozzle plate, however, encounters the drawback in that it is welded directly to the nozzle body, resulting the thermal deformation of a valve body and a valve seat.
The structure as taught in Japanese Patent First Publication No. 6-26419 gives rise to an increase in number of parts and the thermal deformation similar to the above.